Electric vehicle battery cooling using excess cabin air conditioning capacity

ABSTRACT

A battery thermal management system includes a passenger cabin air-conditioning refrigerant loop including at least one evaporator in fluid communication with a chiller and a battery pack coolant loop in fluid communication with the chiller. A controller is configured to determine whether a temperature of the at least one evaporator falls within a predetermined temperature range, and if so to cause a valve to bypass a refrigerant from the air-conditioning refrigerant loop to the chiller. Evaporator temperature is determined by providing at least one evaporator temperature sensor.

TECHNICAL FIELD

This document relates generally to the motor vehicle field and, moreparticularly, to an electric vehicle battery cooling system and relatedmethod.

BACKGROUND

Vehicles are being developed that reduce or completely eliminatereliance on internal combustion engines, with a goal of reducing oreliminating automotive fuel consumption and emissions. Electrifiedvehicles are one type of vehicle currently being developed for thispurpose. In general, electric vehicles differ from conventional motorvehicles because they are selectively driven by one or more batterypowered electric machines. Conventional motor vehicles, by contrast,rely exclusively on the internal combustion engine to drive the vehicle.

A high voltage battery pack typically partially or fully powers theelectric machines and other electrical loads of the electric vehicle.The battery pack includes a plurality of battery cells that must beperiodically recharged to replenish the energy necessary to power theseloads. As is known, during operations such as charging and dischargingthe battery cells generate heat which must be managed. Thus, there is aneed for innovative battery thermal management systems to manage theheat generated by the battery cells.

To address these and other issues, the present disclosure describes anelectric vehicle cooling system utilizing excess cooling capacitygenerated by the vehicle air conditioning (A/C) system, and describesalso a related method for battery thermal management in an electricvehicle.

SUMMARY

In accordance with the purposes and benefits described herein, a batterythermal management system is provided comprising a passenger cabinair-conditioning refrigerant loop comprising at least one evaporator influid communication with a chiller, a battery pack coolant loop in fluidcommunication with the chiller, and a controller configured to determinewhether a temperature of the at least one evaporator falls within apredetermined temperature range, and if so to cause a valve to bypass arefrigerant from the air-conditioning refrigerant loop to the chiller.The controller is further configured to cause the valve to bypass theair-conditioning refrigerant loop refrigerant to the chiller only ondetermining that the battery pack temperature has reached or exceeded apredetermined upper temperature limit.

At least one evaporator temperature sensor is provided to monitor atemperature of the at least one evaporator. In embodiments, the valve isa thermal expansion valve (TXV) which controls introduction of therefrigerant into the chiller. At least one battery pack temperaturesensor may be provided to monitor a temperature of the battery pack. Thepassenger cabin air-conditioning refrigerant loop may further comprise acompressor. In embodiments, the controller is further configured toprevent the compressor from operating above a predetermined maximumoperating pressure.

In another aspect, a method for battery pack thermal management isdescribed, comprising configuring a controller to determine whether atemperature of at least one evaporator of a passenger cabinair-conditioning refrigerant loop falls within a predeterminedtemperature range, further wherein if so the controller is configured tocause a valve to introduce a refrigerant from the passenger cabinair-conditioning refrigerant loop into a chiller in fluid communicationwith both the passenger cabin air-conditioning refrigerant loop and abattery pack coolant loop.

In embodiments, the method includes determining a temperature of the atleast one evaporator by at least one evaporator temperature sensor. Themethod may also include providing a thermal expansion valve (TXV) tocontrol introduction of the refrigerant into the chiller.

Still further, the method may include configuring the controller todetermine whether a battery pack temperature has exceeded apredetermined upper limit. This may be accomplished by providing atleast one battery pack temperature sensor. In embodiments, the methodincludes configuring the controller to cause the valve to introduce theair-conditioning refrigerant loop refrigerant to the chiller only ondetermining that the battery pack temperature has reached or exceededthe predetermined upper limit. In embodiments, the method furtherincludes providing the passenger cabin air-conditioning refrigerant loopincluding a compressor, and further configuring the controller toprevent the compressor from operating above a predetermined maximumoperating pressure.

In the following description, there are shown and described severalpreferred embodiments of the electric vehicle battery cooling system andmethod. As it should be realized, the battery cooling system and methodare capable of other, different embodiments and their several detailsare capable of modification in various, obvious aspects all withoutdeparting from the system and method as set forth and described in thefollowing claims. Accordingly, the drawings and descriptions should beregarded as illustrative in nature and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The accompanying drawing figures incorporated herein and forming a partof the specification, illustrate several aspects of the battery coolingsystem and method and together with the description serve to explaincertain principles thereof. In the drawing figures:

FIG. 1 schematically illustrates an electric vehicle;

FIG. 2 schematically illustrates a battery cooling system according tothe present disclosure; and

FIG. 3 depicts a representative logic for a battery cooling operatingstrategy for the electric vehicle of FIG. 1.

Reference will now be made in detail to the present preferredembodiments of the described battery cooling system and method, examplesof which are illustrated in the accompanying drawing figures.

DETAILED DESCRIPTION

Reference is now made to FIG. 1 which schematically illustrates anelectric or hybrid vehicle 100 of substantially conventional design.Preliminarily, while the present descriptions and drawings primarilydescribe the disclosed electric vehicle heating distribution system andmethod in the context of a battery electric or hybrid vehicle, it willreadily be appreciated by the skilled artisan that the disclosed subjectmatter is readily adaptable to any electric vehicle. At a high level,the term “electric vehicle” as used herein encompasses battery electricvehicles (BEV), hybrid electric vehicles (HEV), plug-in hybrid electricvehicles (PHEV), fuel cell vehicles, or any vehicle having an electricvehicle range. Indeed, the claimed subject matter is applicable to anyvehicle, electric or otherwise, utilizing in combination an A/Crefrigerant loop for passenger cabin climate control and a battery packcoolant loop for battery pack thermal management. Thus, the disclosuresshould not be taken as limiting.

As background, a BEV includes an electric motor, wherein the energysource for the motor is a traction battery. The BEV traction battery isre-chargeable from an external electric grid. The BEV traction batteryis in effect the sole source of on-board energy for vehicle propulsion.A HEV includes an internal combustion engine and an electric motor,wherein the energy source for the engine is fuel and the energy sourcefor the motor is a traction battery. The engine is the main source ofenergy for vehicle propulsion with the HEV traction battery providingsupplemental energy for vehicle propulsion (the HEV traction batterybuffers fuel energy and recovers kinematic energy in electric form). APHEV differs from a HEV in that the PHEV traction battery has a largercapacity than the HEV traction battery and the PHEV traction battery isre-chargeable from the grid. The PHEV traction battery is the mainsource of energy for vehicle propulsion until the PHEV traction batterydepletes to a low energy level at which time the PHEV operates like aHEV for vehicle propulsion.

Returning to FIG. 1, the described electric vehicle 100 includes abattery electric control module 110, a battery pack 120 (in the depictedembodiment a high voltage electric battery), and a transmission controlmodule (TCM) 130 associated with a power inverter 140. The electricvehicle 100 further includes an electric motor 150 which supplies drivepower to a gearbox 160, which in turn supplies a drive force to thevehicle axle/ground engaging tires 170. A vehicle controller 180 maymonitor/control various interactions and functions of theabove-described systems.

Referring now to FIG. 2, the vehicle 100 includes a climate controlsystem 200 including at least a passenger cabin air-conditioning (A/C)subsystem 210 and a battery coolant subsystem 220. Portions of thevarious thermal-management systems may be located within various areasof the vehicle, such as the engine compartment and the cabin, forexample. As will be described, the passenger cabin air-conditioning(A/C) subsystem 210 provides air conditioning of the passenger cabinduring some operating modes, and also may cool the battery pack 120during some operating modes.

The passenger cabin air-conditioning (A/C) subsystem 210 may be avapor-compression heat pump that circulates a refrigerant transferringthermal energy to various components of the climate control system 200.The passenger cabin air-conditioning subsystem 210 may include apassenger cabin refrigerant loop 230 having a compressor 240, anexterior heat exchanger 250 (e.g., condenser), a first interior heatexchanger (e.g., front evaporator 260), a second interior heat exchanger(e.g., rear evaporator 270), an accumulator, fittings, valves, expansiondevices and other components commonly associated with refrigerantsubsystems. The evaporators may each have an associated blower 280. Thecondenser 250 may be located behind the grille near the front of thevehicle, and the front and rear evaporators 260, 270 may be disposedwithin one or more HVAC housings. It is to be understood that heatexchangers labeled as “condenser” may also act as an evaporator if thepassenger cabin air-conditioning (A/C) subsystem 210 is a heat pump. Afan 290 may circulate air over the condenser 250.

The passenger cabin refrigerant loop 230 components are connected in aclosed loop by a plurality of conduits, tubes, hoses or lines. Forexample, a first conduit 300 places the compressor 240 and the condenser250 in fluid communication, a second conduit 310 connects the condenser250 to an intermediate heat exchanger 320, and another conduit 330places the evaporators 260, 270 in fluid communication with theintermediate heat exchanger 320. The front evaporator 260 is connectedwith conduit 330 via conduit 340, and the rear evaporator 270 isconnected with conduit 330 via conduit 350. A first expansion device 360is disposed on conduit 340 and controls refrigerant flow to the frontevaporator 260. The expansion device is configured to change thepressure and temperature of the refrigerant in the subsystem 210. Theexpansion device 360 may be a thermal expansion valve with anelectronically controllable shut-off feature or may be an electronicexpansion valve. A second expansion device 370 is disposed on conduit350 and controls refrigerant flow to the rear evaporator 270. The secondexpansion device 370 may be similar to or different from the firstexpansion device 360. The front evaporator 260 is connected to a returnconduit 380 via conduit 390, and the rear evaporator 270 is connectedwith return conduit 380 via conduit 400. The return conduit 380 connectsbetween the intermediate heat exchanger 320 and the evaporators 260,270. Conduit 410 connects between the intermediate heat exchanger 320and the compressor 240. The intermediate heat exchanger 320 is optional.

The climate control system 200 includes a controller 420 in electroniccommunication with several of the climate-control components. Thecontroller 420 may be the same or may be different from the vehiclecontroller 180.

The dashed lines in FIG. 2 illustrate electrical connections between thecontroller 420 and the components. The controller may interface with thevarious components via a data bus or dedicated wires as described above.The evaporators 260, 270 each include a respective temperature sensor430 and 440 configured to send a signal indicating the temperature ofthe corresponding evaporator to the controller 420. Using thesetemperature signals, and other signals, the controller 420 can determinethe operating conditions of the various components of the climatecontrol system 200.

The battery coolant subsystem 220 includes a chiller 450 which, as willbe described below can be placed in fluid communication with thepassenger cabin refrigerant loop 230, and a third expansion device 460.The battery coolant subsystem 220 may include a supply conduit 470connected to conduit 310 by a fitting and connected to arefrigerant-inlet side 480 of the chiller 450. The expansion device 460may be on the supply conduit 470. The expansion device 460 is configuredto change the pressure and temperature of the refrigerant flowingtherethrough. The expansion device may be a thermal expansion valve(TXV) with an electronically controllable shut-off feature.

The shut-off feature is controlled by the controller 420. The controller420 may instruct the shut-off feature to position the expansion devicein a wide-open position, a fully closed position, or a throttledposition. The throttled position is a partially open position where thecontroller modulates the size of the valve opening to regulate flowthrough the expansion device. The controller 420 and expansion device460 may be configured to continuously or periodically modulate thethrottled position in response to system operating conditions. Bychanging the opening within the expansion device, the controller canregulate flow, pressure, temperature, and state of the refrigerant asneeded. A return conduit 490 connects the battery chiller 450 to thepassenger cabin refrigerant loop 230. The return conduit 490 isconnected to the refrigerant-outlet side 500 of the chiller 450 at oneend and is connect with conduit 350 at the other.

The battery coolant subsystem 220 places the battery pack 120 and thechiller 450 in fluid communication. The battery coolant subsystem 220includes a pump 510 disposed on a first conduit 520 that connectsbetween the battery pack 120 and a coolant-inlet side 530 of the chiller450. A second conduit 540 connects between a coolant-outlet side 550 andthe battery pack 120. A coolant inlet temperature sensor 560 is disposedon conduit 520 near the inlet side 530. The coolant inlet temperaturesensor 560 is configured to output a signal to the controller 420indicating a temperature of the coolant circulating into the chiller450. A coolant outlet temperature sensor 570 is disposed on conduit 540near the outlet side 550. The coolant outlet temperature sensor 570 isconfigured to output a signal to the controller 420 indicating atemperature of the coolant exiting the chiller 450. A battery packtemperature sensor 580 is provided to allow the controller 420 todetermine a battery pack 120 operating temperature.

The battery chiller 450 may have any suitable configuration. Forexample, the chiller 450 may have a plate-fin, tube-fin, ortube-and-shell configuration that facilitates the transfer of thermalenergy without mixing the heat-transfer fluids in the battery coolantsubsystem 220 and the passenger cabin refrigerant loop 230.

The chiller 450 is used to transfer air-conditioner cooling viarefrigerant to a battery coolant to cool the battery pack 120. However,operation of the chiller 450 may cause an increase in passenger cabintemperature, resulting in passenger discomfort. To avoid this situation,by the presently disclosed system and method priority is given topassenger cabin cooling. However, when excess passenger cabinair-conditioning capacity is available, that excess capacity is divertedto cool the battery pack 120 as needed. At a high level, when thecontroller 420 determines by temperature sensors 430, 440 that atemperature of one or both evaporators 260, 270 is determined to bewithin a predetermined lower limit and an upper limit, the controllerwill cause expansion device 460 to allow refrigerant from the passengercabin refrigerant loop 210 to enter the chiller 450. Otherwise, thechiller 450 will not operate.

In the situation where the passenger cabin refrigerant loop 230 isoperating in a reduced reheat mode with one or both evaporators 260, 270at or near the predetermined upper limit and the chiller 450 is notoperating, operation of the chiller can only occur after application ofa predictive method to anticipate a need for battery pack 120 cooling,which is determined by controller 420 determining a battery packoperating temperature via temperature sensor 570. In an embodiment, thecontroller 420 determines whether a predetermined battery pack 120threshold temperature has been reached. If that predetermined batterypack 120 threshold temperature has been reached, the controller 420causes the temperature of one or both evaporators 260, 270 to lower tothe predetermined lower limit and holds that temperature for apredetermined time to store excess cooling capacity in the evaporator260 and/or 270. At that time, the chiller 450 may be operated until thecontroller 420 determines that one or both evaporators 260, 270 havereached the predetermined upper temperature limit. During this process,the vehicle air conditioning system blend door (not shown) functionsnormally to maintain a steady register discharge air temperature,preventing the vehicle occupant(s) from experiencing any temperatureswing.

In more detail, FIG. 3 shows a representative control strategy and/orlogic that may be implemented using one or more processing strategiessuch as event-driven, interrupt-driven, multi-tasking, multi-threading,and the like. As such, various steps or functions illustrated may beperformed in the sequence illustrated, in parallel, or in some casesomitted. Although not always explicitly illustrated, one of ordinaryskill in the art will recognize that one or more of the illustratedsteps or functions may be repeatedly performed depending upon theparticular processing strategy being used. Similarly, the order ofprocessing is not necessarily required to achieve the features andadvantages described herein but is provided for ease of illustration anddescription. The control logic may be implemented primarily in softwareexecuted by a microprocessor-based vehicle, engine, and/or powertraincontroller, such as controller 420. Of course, the control logic may beimplemented in software, hardware, or a combination of software andhardware in one or more controllers depending upon the particularapplication. When implemented in software, the control logic may beprovided in one or more computer-readable storage devices or mediahaving stored data representing code or instructions executed by acomputer to control the vehicle or its subsystems. The computer-readablestorage devices or media may include one or more of a number of knownphysical devices which utilize electric, magnetic, and/or opticalstorage to keep executable instructions and associated calibrationinformation, operating variables, and the like.

At step 600 controller 420 determines a battery pack 120 temperature bytemperature sensor 580 and further ascertains if the battery pack 120temperature is greater than or equal to an upper threshold temperature(T_bh). If not, no action is taken. If so, the controller 420 furtherdetermines at step 610 if the passenger cabin refrigerant loop 230(i.e., the vehicle A/C system) is operating and whether the front and/orrear evaporators 260, 270 are operating. If the evaporators 260, 270 arenot operating, the controller 420 further determines at step 620 whetherthe battery pack 120 temperature is at or below a predetermined limit,in one embodiment being 0° C. If so, the system resets back to step 600.If not, at step 630 the controller 420 causes the passenger cabinrefrigerant loop 210 to operate in chiller mode only, and furtherdetermines that the compressor 240 operates at or below a predeterminedmaximum pressure, in one embodiment being 2350 kPa.

If one or both of the evaporators 260, 270 are operating, at step 640the controller 420 determines whether the evaporators are operatingbetween a predetermined upper and lower temperature limit. If not, thesystem returns to step 600, as no excess cooling capacity is available.

If so, at step 650 the controller 420 causes the expansion device 460 toallow refrigerant from the passenger cabin refrigerant loop 230 to enterthe chiller 450, thus diverting excess cooling capacity from thepassenger cabin refrigerant loop to the battery coolant subsystem 220 tocool the battery. At step 650 a the controller 420 controls theoperation of expansion device 460 to control coolant flow rate into thechiller 450 as a function of evaporator 260 and/or 270 upper temperaturelimit, i.e., as one or both evaporators 260, 270 approach thepredetermined upper temperature limit, coolant flow rate into thechiller 450 is reduced or terminated.

At step 650 b, the controller 420 determines that the compressor 240operates at or below a predetermined maximum pressure, in one embodimentbeing 2350 kPa. The controller 420 further ensures that the maximum heattransfer from the battery pack 120 to the chiller 450 is kept below amaximum chiller heat transfer to reduce any impact to passenger cabincomfort. Since any A/C cooling capacity transfer to the battery pack 120via the chiller 450 will have an impact on cabin temperature, maximumchiller capacity will be an allowable cabin temperature rise (or cabinair temperature degradation) as the result of cooling transfer to thebattery pack. Within the above-described constrictions, coolant flowrate into the chiller 450 controls the chiller capacity, i.e. the heattransfer from the battery pack 120 while maintaining passenger cabincomfort levels, thus meeting customer needs and ensuring customersatisfaction.

The foregoing has been presented for purposes of illustration anddescription. It is not intended to be exhaustive or to limit theembodiments to the precise form disclosed. Obvious modifications andvariations are possible in light of the above teachings. All suchmodifications and variations are within the scope of the appended claimswhen interpreted in accordance with the breadth to which they arefairly, legally and equitably entitled.

What is claimed:
 1. A battery thermal management system, comprising: apassenger cabin air-conditioning refrigerant loop comprising at leastone evaporator in fluid communication with a chiller; a battery packcoolant loop in fluid communication with the chiller; and a controllerconfigured to determine whether a temperature of the at least oneevaporator falls within a predetermined temperature range, and if so tocause a valve to bypass a refrigerant from the air-conditioningrefrigerant loop to the chiller.
 2. The battery thermal managementsystem of claim 1, further including at least one evaporator temperaturesensor.
 3. The battery thermal management system of claim 1, wherein thevalve is a thermal expansion valve (TXV) which controls introduction ofthe refrigerant into the chiller.
 4. The battery thermal managementsystem of claim 2, further including at least one battery packtemperature sensor.
 5. The battery thermal management system of claim 4,wherein the controller is further configured to cause the valve tobypass the air-conditioning refrigerant loop refrigerant to the chilleronly on determining that the battery pack temperature has reached orexceeded a predetermined upper limit.
 6. The battery thermal managementsystem of claim 1, wherein the passenger cabin air-conditioningrefrigerant loop further comprises a compressor.
 7. The battery thermalmanagement system of claim 6, wherein the controller is furtherconfigured to prevent the compressor from operating above apredetermined maximum operating pressure.
 8. An electric vehicleincluding the battery thermal management system of claim
 1. 9. In anelectric vehicle, a method for battery pack thermal management,comprising: configuring a controller to determine whether a temperatureof at least one evaporator of a passenger cabin air-conditioningrefrigerant loop falls within a predetermined temperature range; andconfiguring the controller to, if so, cause a valve to introduce arefrigerant from the passenger cabin air-conditioning refrigerant loopinto a chiller in fluid communication with both the passenger cabinair-conditioning refrigerant loop and a battery pack coolant loop. 10.The method of claim 9, including determining a temperature of the atleast one evaporator by at least one evaporator temperature sensor. 11.The method of claim 9, including providing a thermal expansion valve(TXV) to control introduction of the refrigerant into the chiller. 12.The method of claim 10, further including by the controller determiningwhether a battery pack temperature has exceeded a predetermined upperlimit.
 13. The method of claim 12, including determining the batterypack temperature by at least one battery pack temperature sensor. 14.The method of claim 12, further including configuring the controller tocause the valve to introduce the air-conditioning refrigerant looprefrigerant to the chiller only on determining that the battery packtemperature has reached or exceeded the predetermined upper limit. 15.The method of claim 9, further including providing the passenger cabinair-conditioning refrigerant loop including a compressor.
 16. The methodof claim 15, further including configuring the controller to prevent thecompressor from operating above a predetermined maximum operatingpressure.
 17. A battery thermal management system, comprising: apassenger cabin air-conditioning refrigerant loop comprising at leastone evaporator in fluid communication with a chiller; a battery packcoolant loop in fluid communication with the chiller; and a controllerconfigured to determine whether a temperature of the at least oneevaporator falls within a predetermined temperature range and whether abattery pack temperature has reached or exceeded a predetermined upperlimit, and if so on request to cause a valve to introduce a refrigerantfrom the air-conditioning refrigerant loop into the chiller.
 18. Thebattery thermal management system of claim 17, further including atleast one evaporator temperature sensor.
 19. The battery thermalmanagement system of claim 17, wherein the valve is a thermal expansionvalve (TXV) which controls introduction of the refrigerant into thechiller.
 20. The battery thermal management system of claim 17, furtherincluding at least one battery pack temperature sensor.